Precision boring, typically with a diameter tolerance of less than 0.001 inch, is a generally costly and difficult operation, not easily adapted to production line or high efficiency use. The difficult nature of such machining operations arises from several error sources which significantly affect the accuracy of such boring processes and are inherent in such operations as previously practiced. One major area of such errors results from the difference between the static measurement of tool boring diameter and the actual bore which the tool produces in operation. Such differences can result from many factors including wear and contamination of the cutting surface both before and during a cut, the varying nature of the materials forming the cutting surface, as well as the materials which define the overall tool rigidity and run-out error. The nature of the workpiece can have a significant effect in the variation of actually produced bore diameter. The temperature of both the cutting tool and the workpiece will affect the resulting bore. A second major area of difficulty results from errors attributable to rechucking of a machining tool in the drive spindle. These rechucking errors are due in part to variation in the relative position of tool and spindle, variations in local surface geometry of tool and spindle, variations in drawbar pull as well as the presence of contaminants between chucking surfaces.
In one type of high accuracy boring operation a plurality of passes through the same bore are produced to achieve gradually increasing bore diameters toward a finaly desired diameter. For each pass of increased diameter, a minimum amount of material must be removed in order that the cutting edge can operate below the region of surface hardening. Thus an accurate finished cut can not be made by a process of very small increments. The final machining pass must remove substantial material and its ultimate accuracy subject to some uncertainty. Rejection rates for final bores can thus be high.
Some of these inefficiencies can be avoided by gauging the bore after each pass to determine its actual diameter and, using an adjustable boring tool, make an adjustment to the tool based upon the desired increase in bore diameter. Such operations are still undesirably slow, involving time consuming man-machine interactions that interrupt production line activity and subject the adjustment procedure to operator error.